   "Implements oplus from the Next Closure Algorithm."
   [G clop A i]
   (clop (set (conj (filter #(contains? A %) (subelts G i))
-		   i))))
+                   i))))
 
 (defn next-closed-set-in-family
   "Computes next closed set as with next-closed-set, which is in the

  [clop A]
  (let [clop-A (clop A)]
    (loop [left     [A],                ;yet to consider
           minimals []]                 ;minimals elements already found
      (if (empty? left)
        (distinct minimals)
        (let [next (first left)]

  (if (empty? sets)
    #{[]}
    (set-of (conj t x) [t (apply cross-product (butlast sets))
                        x (last sets)])))

(defn disjoint-union
  "Computes the disjoint union of sets by joining the cross-products of the
